32 INTRODUCTION. 



points, which it may be useful to impress on those 

 who purpose to become observers of nature. And 

 first as regards the importance of observing accu- 

 rately. The value of the facts which we propose to 

 collect must rest primarily on the correctness with 

 which they are noted. And though it may seem 

 hardly necessary to insist on this, yet in fact it is so, 

 from the numberless errors into which persons are 

 led every dayj in respect of the objects that fall 

 under their notice, from not giving them a sufficient 

 examination. If we are not habituated to looking 

 closely at objects, we are apt to be misled by first 

 appearances, and to mistake one thing for another. 

 Thus we have known many persons mistake the 

 " large hop-like fruit" of the wich-elm, so conspi- 

 cuous in the latter part of the spring, for leaves ; 

 and they would scarcely believe that the tree was not 

 in full leaf, until it had been made evident to their 

 senses, by plucking a branch, that what they saw was 

 merely the expanded seed-vessel, the true leaf-buds 

 being as yet scarcely evolved. Had one of these 

 individuals been requested by a botanical friend to 

 register the dates of the leafing of the different trees 

 in his neighbourhood, he would have been liable in 

 this instance to have registered a false fact, without 

 the slightest suspicion of its being incorrect. In 

 like manner the fall of the floral leaves, or bractece, 

 of the lime, towards the end of August or beginning 

 of September, might lead a hasty observer to ima- 

 gine that the true leaves were beginning to fall at 

 that early period. How often again are the great 

 flies, which enter our apartments so frequently in 



